The effects of the intervention on the primary outcome measures (VAS and 4DSQ) and the secondary outcome measures (NHL, SF-36 and MAF) were estimated using analysis of covariance with baseline value as a covariate. Data analysis was be performed according to the intention-to-treat principle. Medical consumption was measured using the Cost Diary for medical consumption. Patients recorded their absenteeism and healthcare consumption, such as consulting a GP, hospital, paramedic facilities and alternative medicine. Medication intake was recorded at the start and the end of the study. We used standardised Dutch prices (guide cost research 2009), whereas medication costs were calculated according to the Dutch Pharmaco Therapeutic Compass. Costs by absenteeism were calculated according to the Friction Cost method.